Fastener joint with sealing gasket

ABSTRACT

A joint comprising: a first component having a face and a bore defined by a bore wall; a second component; a fastener joining the first component to the second component, the fastener comprising a head and a shaft protruding from the head; and a polysulphide gasket comprising a ring which is compressed between the head of the fastener and the face of the first component; and a collar between the shaft of the fastener and the bore wall. The gasket comprises a ring of sealing material surrounding a hole for receiving a fastener, the sealing material comprising an at least partially cured polysulphide sealant. The gasket has a region of increased thickness positioned towards the inner periphery of the ring which flows to form the collar.

The present application is a divisional of U.S. application Ser. No.12/680,911, filed Mar. 31, 2010 and is national phase ofPCT/GB2008/050968, filed Oct. 20, 2008, and claims priority from,British Application Number 0720705.3, filed Oct. 23, 2007, thedisclosures of which are hereby incorporated by reference herein intheir entirety.

FIELD OF THE INVENTION

The present invention relates to a joint with a sealing gasket, a gasketfor use in such a joint, and a method of manufacturing such a joint.

BACKGROUND OF THE INVENTION

EP 1548083 A1 describes a sealing material for use in sealing joints.The sealing material comprises an at least partially cured polysulphidesealant and a reinforcing element. The sealing material is provided inthe form of a sheet of uniform thickness. The sheet is placed betweenthe mating surfaces of the components in the manner of a gasket, and thecomponents are then fastened together, for example with rivets or bolts.

While the sealing material will to some degree move away from thefasteners as they are tightened, the curing of the sealant material andthe presence of the reinforcing element will, in general, prevent thesealing material from moving entirely away from the vicinity of thefasteners.

U.S. Pat. No. 3,022,870 describes a fastener joint with aself-sustaining adherent polysulphide film forming a fluid-tight sealbetween a pair of metal plates.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a joint comprising: a firstcomponent having a face and a bore defined by a bore wall; a secondcomponent; a fastener joining the first component to the secondcomponent, the fastener comprising a head and a shaft protruding fromthe head; and a polysulphide gasket comprising a ring which iscompressed between the head of the fastener and the face of the firstcomponent; and a collar between the shaft of the fastener and the borewall.

A second aspect of the invention provides a method of manufacturing ajoint, the method comprising:

-   -   mounting a gasket on a fastener; the fastener comprising a head        and a shaft protruding from the head, and the gasket comprising        an at least partially cured polysulphide sealing material;    -   inserting the shaft of the fastener through a first component        and at least partially through a second component until the        gasket engages the first component; and    -   compressing the gasket between the head of the fastener and the        first component whereby the sealing material flows along the        shaft of the fastener and forms a collar between the shaft of        the fastener and the first component.

In contrast with the gaskets in EP 1548083 A1 and U.S. Pat. No.3,022,870, in which the sealant material forms a seal between the matingpairs of components, the gasket of the present invention forms a collarbetween the shaft of the fastener and the bore wall.

Preferably the collar of the gasket engages both the shaft of thefastener and the bore wall.

Preferably the collar of the gasket forms a bond with the shaft of thefastener and/or the bore wall.

Preferably the ring forms a bond with the head of the fastener and theface of the first component.

The head of the fastener may comprise a non-tapered button-head, or morepreferably the bore comprises a tapered opening and the head of thefastener comprises a tapered head which is received in the taperedopening.

The gasket may be un-reinforced, or more preferably the gasket furthercomprises a reinforcing element such as a fabric. Typically the gasketcomprises a matrix-rich region which contains a lower than averagedensity of reinforcement, for instance on an outer surface of thegasket.

Any suitable reinforcing material may be used, for example glass,carbon, aramid, metal (especially stainless steel) or polyamide.

To protect the structure of an aircraft in the event of a lightningstrike, the electrical conductivity through the structure and acrossjoints needs to be controlled. This is also important to ensure the safedissipation of static electricity. In the case of sealed joints, thereis a requirement to prevent voids between the fastener and the structurewhich can be heated by high electrical currents, expand and cause damageto the surrounding structure.

The current solution for sealing and protecting structure from lightningstrike is to prevent air voids by using wet assembled sealed joints andto provide a low impedance path between two surfaces or parts, usuallythrough the use of bonding leads. However, bonding leads can fail(break) creating a spark hazard, which is unacceptable particularly inareas of the aircraft containing fuel vapour. Moreover, a large spaceenvelope is required to install and maintain bonding leads.

Optionally the polysulphide material forming the gasket may be loadedwith conductive particles. In this case the gasket will provide anelement of protection from lightning strike by forming an electricalpath between the components without air voids. The conductive particlesmay comprise carbon black or metals such as silver. However carbon blackmay not be sufficiently conductive and silver will reduce the mechanicalproperties of the polysulphide, especially when at higherconcentrations. Therefore most preferably the conductive particles arecarbon nanotubes.

Optionally the reinforcing material may also be formed by a conductivefabric, such as metal, for purposes of lightning protection.

In order to increase the sealing material that flows along the shaft ofthe fastener, the gasket may have a region of increased thicknesstowards its inner periphery. This region may extend only partly roundthe circumference of the ring (for instance in a series of discretelocations) or may extend around the entire circumference of the ring.Typically the region of increased thickness includes a matrix-richprotrusion which contains a lower than average density of reinforcement.

A further aspect of the invention provides a gasket for sealing afastener joint, the gasket comprising a ring of sealing materialsurrounding a hole for receiving a fastener, the sealing materialcomprising an at least partially cured polysulphide sealant with aregion of increased thickness positioned towards the inner periphery ofthe ring.

The gasket is specially adapted for use in the first and second aspectsof the invention, since the region of increased thickness provides thenecessary material to flow along the shaft of the fastener.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theaccompanying drawings, in which:

FIG. 1 is a plan view of a gasket;

FIG. 2 is a cross-section through the gasket;

FIG. 3 is an enlarged cross-section through part of the gasket;

FIG. 4 is a cross-sectional view of a joint on an aircaft, before thesealant material has flowed along the shaft of the bolt;

FIG. 5 shows the bolt being pushed into the joint; and

FIG. 6 shows the joint after the sealant material has flowed along theshaft of the bolt.

DETAILED DESCRIPTION OF EMBODIMENT(S)

A gasket 1 shown in FIGS. 1-3 comprises a ring of sealing material withan outer periphery 2, and an inner periphery 3 surrounding a hole 4.

The sealing material comprising an at least partially cured polysulphidesealant 5, and a layer of fabric reinforcement 6 shown in cross-sectionin FIGS. 2 and 3. The gasket has a ring-shaped protrusion 7 which ispositioned towards the inner periphery 3 of the ring, and extends aroundthe entire circumference of the ring as shown in FIG. 1. The protrusion7 contains substantially none of the reinforcing fabric as shown inFIGS. 2 and 3.

The gasket is manufactured by the following process. First, a paste ofpolysulphide material is mixed with a curing agent such as manganesedioxide. Various suitable sealant materials are described in EP 1548083A1, the contents of which is incorporated herein by reference. By way ofexample, the material may comprise Chemetall MC238-A1/2 or PRC-De SotoInternational PR1770C12. Optionally the paste of polysulphide materialmay be filled with conductive particles, most preferably carbonnanotubes, for purposes of lightning protection.

A woven cloth of glass-fibre is then impregnated with the polysulphidesealant by a conventional calendering process. The calendering processproduces matrix-rich regions 8,9 shown in FIG. 3. Then the sheet isstamped to cut out the ring-shaped profile of the gasket which is placedbetween a pair of mould tools shaped to give the required shape to theprotrusion 7. The ring is compressed between the mould tools and heatedto a lightly raised temperature (no greater than 60° C.) to fully orpartially cure the polysulphide material. Completion of the curingprocess may occur before or after assembly of the joint.

A method of sealing a fastener joint with the gasket 1 is shown in FIGS.4-6. First, the gasket 1 is mounted on the tapered head 10 of a bolt.The shaft 11 of the bolt is then passed through a pair of components 12,13 as shown in FIG. 4, and a nut 14 is screwed onto the threaded distalend 15 of the shaft 11. As the nut is screwed tight, the gasket engagesa tapered opening 16 in the first component 12 as shown in FIG. 5. Atthis point the gasket is un-deformed. As the nut is tightened further;the gasket 1 becomes compressed between the tapered head 10 of the boltand the wall of the tapered opening 16. Unexpectedly, this pressurecauses the polysulphide sealing material in the matrix-rich regions 8,9and the protrusion 7 to flow along the shaft 11 of the fastener to forma cylindrical collar 18 between the shaft 11 and the wall of thecylindrical bore 19 in the first component 12 as shown in the left-handside FIG. 6. The right-hand side of FIG. 6 shows the gasket in itsun-flowed state, for comparison purposes. This can be contrasted withgaskets formed with polytetrafluoroethylene (PTFE) which tend to flowoutwardly instead of flowing along the shaft 11.

Conceivably, if the first component 12 is thin then the sealing materialmay flow as far as the second component 13. After a period of time, thesealing material bonds to the opposing surfaces of the tapered head 10,tapered opening 16, shaft 11 and the wall of the cylindrical bore 19 toform a fluid-tight seal.

Although the invention has been described above with reference to one ormore preferred embodiments, it will be appreciated that various changesor modifications may be made without departing from the scope of theinvention as defined in the appended claims.

1. A joint comprising: a first component having a face and a boredefined by a bore wall; a second component; a fastener joining the firstcomponent to the second component, the fastener comprising a head and ashaft protruding from the head; and a polysulphide gasket comprising aring which is compressed between the head of the fastener and the faceof the first component; and a collar between the shaft of the fastenerand the bore wall
 2. The joint of claim 1, wherein the gasket furthercomprises a reinforcing element.
 3. The joint of claim 2, wherein thereinforcing element comprises a fabric.
 4. The joint of claim 1, whereinthe bore comprises a tapered opening and the head of the fastenercomprises a tapered head which is received in the tapered opening. 5.The joint of claim 1, wherein the polysulphide material forming thegasket is loaded with conductive particles.
 6. A method of manufacturinga joint, the method comprising: mounting a gasket on a fastener; thefastener comprising a head and a shaft protruding from the head, and thegasket comprising an at least partially cured polysulphide sealingmaterial; inserting the shaft of the fastener through a first componentand at least partially through a second component until the gasketengages the first component; and compressing the gasket between the headof the fastener and the first component whereby the sealing materialflows along the shaft of the fastener and forms a collar between theshaft of the fastener and the first component.
 7. The method of claim 6wherein the gasket comprises a region of increased thickness positionedtowards the inner periphery of the gasket which flows along the shaft ofthe fastener.
 8. The method of claim 7 wherein the region of increasedthickness extends around the entire circumference of the gasket.
 9. Themethod of claim 6 wherein the gasket further comprises a reinforcingelement.
 10. The method of claim 9 wherein the gasket comprises amatrix-rich region which contains a lower than average density ofreinforcement and which flows along the shaft of the fastener.
 11. Anaircraft comprising a joint according to any of claim 1.